Back-up warning system and timing circuit therefor



June 7, 1960 D. E. ATKINSON BACK UP WARNING SYSTEM AND TIMING CIRCUIT THEREFOR Filed April 1, 1957 Fll3 /2 &EE .TIMING cmcun- /3\ .L Q DIRECTION L: $EN5ITIVE SWITCH TO OSCILATOR VOLT S 4 RELAY ,a-cAPAcnon TIME.

MOTION INVENTOR. Duane E. 14/44/7500 United States Patent- BACK-UP WARNING SYSTEM AND TIMING CIRCUIT THEREFOR Duane E. Atkinson, 102 Fey Drive, Burllngame, Calif.

Filed Apr. 1, 1957, Ser. No. 649,849

4 Claims. (Cl. 340-70) This invention relates generally to a back-up warning system and timing circuit therefor, and more particularly to a system which includes an intermittently operated direction responsive switch for activating a warning device or alarm, and a timing circuit for use in said system and serving to prevent drain on the power source if the switch remains closed for a prolonged period of time.

As is well known, trucks, tractors and like motor vehicles are provided in many instances with signal or alarm means which provide a characteristic warning when the vehicle moves backwardly. For example, on construction projects such signal or alarm means are employed on trucks, tractors, etc. to minimize collisions and personal hazards.

In many of these alarm means, direction responsive switch means are provided which are intermittently closed to operate an associated warning device or alarm as the vehicle moves backwardly. However, when the vehicle is stopped with the switch closed, the warning device or alarm is continuously energized causing a disconcerting noise and an excessive power drain on the battery.

The warning signal or alarm means is in general not directional in nature. It is, therefore, difiicult to ascertain from which direction the vehicle is approaching. As a result, it is possible to become confused when several vehicles are moving rearwardly in a general area.

In most warning devices, the frequency range of the warning alarm or signal is relatively wide. Thus, to generate a sound which can be heard over the background noise requires a relatively large amount of power.

It is an object of the present invention to provide a novel timing device which serves to deenergize the warning signal or alarm a predetermined period of time after the switch is closed.

It is another object of the present invention to provide a novel timing circuit.

It is still a further object of the present invention to provide an improved back-up warning system.

These and other objects of the invention will be more clearly understood from the following description when read in conjunction with the accompanying drawing.

Referring to the drawing:

Figure l is a schematic block diagram of a back-up warning system;

Figure 2 is a circuit diagram of a suitable transistor timing circuit;

Figure 3 shows the voltage and current waveforms at various points in the timing circuit; and

Figure 4 is a plan view schematically showing a truck with the sound emanating in a predetermined pattern.

Referring to Figure l, a typical direction responsive intermittently operated switch 11 is schematically illustrated. The switch illustrated is of the type described in Patent No. 2,754,384, and is driven by a shaft 12 which is connected to a suitable rotating member of the vehicle with which it is associated. A cam assembly (not illustrated) operates contacts to make and break a circuit as the vehicle is moving in the reverse direction but to maintain an open circuit when the vehicle moves in a forward direction. The switch 11 is connected to apply power from the battery 13 to the timing circuit 14, to be presently described in detail. The timing circuit controls the energization of the signal or alarm device and deenergizes the same a predetermined period of time after the switch is closed.

Preferably, the warning signal or alarm device is of the electronic type wherein an oscillator 16 generates a predetermined frequency which is applied to a speaker 17. I have found that in most instances a frequency in the neighborhood of 1000 cycles is suitable for a warning device. The sound generated may be heard over the background noise and is easily distinguishable thereover. The advantage of generating a relatively pure signal or one having a limited frequency range is that all of the power is generated at a particular frequency and less power is required to obtain a volume which overrides the background noise. As a consequence, less power is required.

The device 17 which forms the sound is preferably of a type which has directional characteristics such as shown at 18, Figure 4. Preferably, the characteristics are such that the sound is emitted over a predetermined pattern. For example, in Figure 4 the sound is emitted to the rear of the truck and very little sound is emitted outwardly from the sides thereof. Thus, a man standing at the point 19 does not hear this sound from the truck shown. Consequently, he is not alarmed by the truck. With a proper pattern, when an individual hears the sound he is in a danger zone, whereas if no sound is heard he is in a safe zone. This permits many vehicles to be operated in one area without the possibility of confusion. If the sound emitted does not have directional characteristics as described, then the man standing at 19 may hear the sound 18, and being relatively close this sound will mask out any sound from another truck approaching from another direction. Thus, it is seen that one of the elements of this invention is that the sound is directed to the area of danger in a predetermined pattern. Another element of importance is that a relatively constant frequency is generated whereby all of the electrical power is converted into sound of a predetermined frequency, therefore making it possible to get the desired volume with realistic power requirements.

Referring now to Figure 2, a suitable transistor timing circuit is illustrated. The switch 11 serves to connnect the timing circuit to the battery 13 as previously described. The timing circuit controls the energization of a relay 21 which is connected to the oscillator or other power source which energizes the signal or alarm device. Transistors 22 and 23 have their collector connected to the common line 24. The base of the transistor 23 is connected to ground. The base of the transistor 22 is connnected to the emitter of the transistor 23 through the serially connected resistors 26 and 27. A capacitor 28 is connected between the common junction of the resistors 26 and 27 and the line 24. The relay coil is connected in the emitter circuit of the transistor 22, having one end connected to the emitter and the other to ground. A resistor 29 is connected between line 24 and ground.

Operation of the timing circuit is as follows: When the switch 11 is closed, the voltages applied to the terminals of the transistor 22 are such that the transistor acts as an amplifier and current flows through the relay coil. The base, at the instant the switch is closed, is at the potential on the line 24, Figure 3A. Figure 3B shows the relay current after the switch is closed. Thus, it is noted that the current remains relatively constant for a short period of time and then begins to decrease ex- 3 ponentially. The voltage on the capacitor is also plotted as a function of time, Figure 30. It is noted that the capacitor instantaneously begins to charge. As the capacitor charges, it varies the voltage between the base and collector of transistor 22 in a manner which tends to bias the transistor toward cut-off, the emitter current being reduced as shown in Figure 38. After a predetermined period of time, the emitter current is reduced to a point 31, Figure 3B. At this point, the relay opens and the power to the signal or alarm means is cut off. The condenser continues to charge and the emitter current continues to decrease exponentially. As long as the switch remains on, small emitter currents will continue to flow and the capacitor voltage will exponentially approach the battery voltage.

The instant the switch 11 is open, the transistor 23 is biased to amplify and the capacitor 28 discharges in the path including resistor 27 and the emitter and collector of transistor 23. The base of the transistor 23 is connected to one side of the capacitor through the resistor 29. If the switch should close before the capacitor 28 is completely discharged, the relay may or may not be operated depending upon the charge on the capacitor 28.

After the condenser has discharged sufficiently, the cycle of operation is repeated when the switch 11 is closed. The resistors 26 and 27 serve to control the rate of charge and discharge of capacitor 28. Thus, by varying the resistor 26, the time during which the relay is energized may be controlled while by controlling the resistor 27 the time during which the timing circuit is inactive may be controlled.

In one particular example, apparatus was constructed in which the switch 11 was of the type described in said patent, No. 2,754,384. The timing circuit 14 was of the type shown in Figure 2. The battery 13 and the various components had the following values: The battery 13 was a 12 volt battery. Transistors 22 and 23 were p-n-p junction transistors, type 2N255. Resistors 26 and 27 were 22 ohms each. Resistor 29 was 1000 ohms. The capacitor 28 was 100 microfarads. The relay coil had a resistance of approximately 78 ohms.

The oscillator 16 operated at 1000 cycles and was a transistor multivibrator. The speaker 17 was of a type known as a folded exponential horn with compression type driver and served to emit the energy in a pattern of the type shown at 18. The apparatus was installed on vehicles and operated in the field on a construction project. It was found that the approach of a rearwardly moving vehicle could easily be heard and that only vehicles so approaching a given point were heard while vehicles moving in other directions were not heard because of the directivity of the horn. The power required was substantially less than the power required for a conventional type automobile horn.

I claim:

1. A backup warning system comprising an intermittently operated direction sensitive switch, alarm means, a source of power for energizing said alarm means, said switch serving to control the application of power to said alarm means, and a timing circuit comprising first and second transistors each having emitter, base and collector electrodes, said collector electrodes being interconnected, the base connection of the first transistor being resistively connected to the emitter connection of the second transistor, the base connection of the second transistor being connected to ground, the emitter connection of the first transistor being connected to ground through a relay coil, a capacitor connected between the collector electrodes of said transistor and the resistive connection between the base and emitter electrodes, and a resistor connected in shunt with the input terminals of said circuit, said timing means serving to deenergize the alarm means a predetermined period of time after power is applied thereto.

2. A back-up warning system comprising a loud speaker, a source of power for energizing said loud speaker with power having a'predetermined narrow band of frequencies, said loud speaker being of the type which emits sound in a pattern dependent upon the applied frequency, an intermittently operated direction sensitive switch for controlling the application of power to said loud speaker, and timing means connected to said switch for de-energizingthe loud speaker a predetermined period of time after power is applied thereto.

3. A back-up warning system comprising a loud speaker, a source of power for energizing said loud speaker with power having a narrow band of frequencies, said loud speaker serving to emit sound in a pattern dependent upon frequency, an intermittently operated direction sensitive switch for controlling the application of power to said loud speaker, and a timing circuit comprising first and second transistors each having emitter, base and collector electrodes, said collector electrodes being interconnected, the base connection of the first transistor being resistively connected to the emitter connection of the second transistor, the base connection of the second transistor being connected to ground, the emitter cor. action of the first transistor being connected to ground through a relay coil, a capacitor connected between the collector electrodes of said transistor and the resistive connection between the base and emitter electrodes, and a resistor connected in shunt with the input terminals of said circuit, the relay coil of said timing means being connected to de-energize the loud speaker means a predetermined period of time after power is applied thereto.

4. A back-up warning system comprising alarm means, a source of power for energizing said alarm means, an intermittently operated direction sensitive switch for controlling the application of power to said alarm means, and a timing circuit including at least one transistor having emitter, base, and collector electrodes, timing means connected to control the conduction of said transistor whereby said transistor is cut off a predetermined period of time after the timing circuit is energized, whereby the alarm means is deenergized a predetermined period of time after power is applied thereto.

References Cited in the file of this patent UNITED STATES PATENTS 2,074,875 Von Voigtlander Mar. 23, 1937 2,288,458 Jeffers June 30, 1942 2,306,590 Chambers Dec. 29, 1942 2,354,699 Owens Aug. 1, 1944 2,431,117 Hadley Nov. 18, 1947 2,576,585 Fleming Nov. 27, 1951 2,583,328 Diamond Jan. 22, 1952 2,636,931 Krom Apr. 28, 1953 2,718,613 Harris Sept. 20, 1955 2,754,384 Atkinson July 10, 1956 2,775,751 Gordon et al. Dec. 25, 1956 

